Note that the afferent pathways common to the pupillary light reflex and menace response (up to the level of the proximal optic tract) are colored in lighter shades. As a result, menace testing in young patients may result in a false negative result, as the animal does not blink even though it can see.įigure 16-2 Anatomic pathway of the menace response: The afferent component of the response is relayed from the retina (1) by the optic nerve (2), through the optic chiasm (3), optic tract (4), lateral geniculate nucleus (5) and optic radiation (6) to the visual cortex (7) located in the occipital lobe. It is usually present by 5 to 7 days in foals and calves. Therefore this response may not become fully developed until 10 to 12 weeks of age in some small animals. The complexity of this pathway implies that the resulting blinking is not a reflex but a learned response. It is assumed that the visual cortex projects to the motor cortex, which in turn projects via the internal capsule and crus cerebri to the facial nuclei in the medulla, and from there the facial nerve (CN VII) relays the efferent signal to the eyelid muscles. The afferent component of the response is relayed by the optic nerve, through the optic chiasm, optic tract, lateral geniculate nucleus (LGN), and optic radiation to the visual cortex located in the occipital lobe. The anatomic pathways of the afferent and efferent components are depicted in Figure 16-2. The normal response to this threat is a rapid blink and closure of the palpebral fissure. To eliminate stimulation due to air movement or touching of hair, the menacing gesture may be made behind a transparent glass or plastic sheet. This eliminates the possibility of a blinking response generated by the visual, untested eye. Table 16-1 Summary of the Neuroophthalmologic ExaminationĬN II, optic chiasm, optic tract, lateral geniculate nucleus, optic radiation, visual and motor cortex, facial nucleus and nerve cerebellumĬN II, optic chiasm, proximal optic tract, CN III, sympathetic nerves, diencephalon-mesencephalon (pretectal and oculomotor nuclei)ĬNs III, IV, VI, vestibular system, brainstemĬN VIII-brainstem and vestibular system-CNs III, IV, VIįigure 16-1 The menace response of the right eye is tested while the left eye is being covered. This chapter reviews the examination, clinical signs, and diseases of the neuroophthalmologic patient. Therefore the workup of the neuroophthalmologic patient requires comprehensive neurologic and systemic examinations, in addition to a thorough neuroophthalmologic examination (Table 16-1). In addition, significant parts of the CNS are devoted to vision processing and ocular control.
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